1. Field of Invention
This invention relates to helicopter blades and more particularly to helicopter blades of the type intended to be used in high speed flight commercial helicopters which will take off and land much of the time in ground-effect mode and including a selectively shaped tip and selected twist to accommodate this mode and other normal helicopter operating modes in improved fashion.
2. Description of the Prior Art
Swept tips are known in the helipcopter blade art, for example, in Giles U.S. Pat. No. 3,399,731, Jepson U.S. Pat. No. 3,822,105 and Monteleone U.S. Pat. No. 3,721,507, but none of this prior art has the selectively-shaped tip, twist and camber as the improved blade taught herein. For example, Giles has neither twist nor camber and Monteleone is basically a 20.degree. swept tip without taper. Further, the tip of the Giles blade ends in a plane perpendicular to the swept or tip axis and his swept tip airfoil cross sections are also perpendicular to the swept axis, producing very low Reynolds Numbers because of the small tip chord parallel to the wind, resulting in high drag coefficients. The tip of my blade, and its airfoil cross section, are perpendicular to the blade span axis.
While other prior art patents such as the aforementioned Jepson and Monteleone patents, and Balch U.S. Pat. No. 3,728,045 teach selectively-shaped helicopter blades, there is no known prior art teaching an improved blade of the type taught herein having the selectively-shaped tip, twist and other features described in greater particularity hereinafter to achieve the advantages which will be described.